Method for avoiding handover failure

ABSTRACT

Methods for avoiding handover failure are provided. The method includes determining, by a source Base Station (BS), to perform a handover of a User Equipment (UE); determining, by the source BS, whether a target BS connects with a user plane node serving the UE at the source BS; and releasing resources, when the target BS does not connect with the user plane node serving the UE at the source BS.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to ChinesePatent Application No. 201110202644.5, which was filed in the StateIntellectual Property Office of the Peoples Republic of China on Jul. 5,2011, the entire disclosure of which is incorporated herein byreference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to mobile communication, andmore particularly, to a method for avoiding handover failure in a mobilecommunication system.

BACKGROUND OF THE INVENTION

System Architecture Evolution (SAE) is the core network architecture ofthe 3^(rd) Generation Partnership Project's (3GPP's) Long Term Evolution(LTE) wireless communication standard. Specifically, SAE is an evolutionof a General Packet Radio Service (GPRS) core network, which reducestime delay and costs for operators, and provides a higher user datarate, higher system capacity, and better coverage.

FIG. 1 is a diagram illustrating a conventional SAE system.

Referring to FIG. 1, the conventional SAE system includes a UserEquipment (UE) 101, i.e., a terminal device, for receiving data, anEvolved Universal Terrestrial Radio Access Network (E-UTRAN) 102, aMobility Management Entity (MME) 103, a Service GateWay (SGW) 104, aPacket data network GateWay (PGW) 105, a Policy and Charging RuleFunction (PCRF) controller 106, a Serving GPRS Support Node (SGSN) 108,and a Home Subscriber Server (HSS) 109.

The E-UTRAN 102 is a wireless access network including a macro EvolvedNodeB (eNB) that provides an interface for accessing the wirelessnetwork for the UE 101.

The MME 103 is responsible for managing mobile contexts, sessioncontexts, and security information of the UE 101, and the SGW 104 ismainly used for providing functions of a user plane. Alternatively, theMME 103 and the SGW 104 may be embodied a single physical entity.

The PGW 105 is responsible for charging and legal monitoring, etc., andmay also be embodied in a single physical entity with the SGW 104. ThePCRF 106 provides Quality of Service (QoS) policies and chargingcriterions.

The SGSN 108 is a network node device for providing routing for thetransmission of data in the Universal Mobile Telecommunications System(UMTS).

The HSS 109 is a home sub-system of the UE 101, for protecting userinformation, such as a current location, an address of a server node,user security information, and packet data context of the UE 101.

Along with enhancements of a service data rate of the UE 101, operatorsprovide a new technology, i.e., Selected IP Traffic Offload (SIPTO).That is, when accessing a specific service, the UE 101 switches to anaccess point from the wireless access network, which is closer, in themovement procedure, to effectively reduce cost for the transmissionnetwork, and provide better service experiences for high data rate.

More specifically, 3GPP presents the network-supported SIPTO and theability of Local Internet Protocol Access (LIPA). In the SIPTO, when theUE 101 accesses the Internet or other extra networks through a Homeevolved NodeB (HeNB), Home NodeB (HNB), or a macro eNB, the network mayselect or re-select a user plane node which is closer to the wirelessaccess network for the UE 101.

Although LIPA provides that when the UE 101 accesses a home network oran intra-company network through the HeNB or HNB, and the LIPA isexecuted, a user plane node close to the HNB or in the HeNB/HNB accessnetwork may be selected or re-selected for the UE 101. The user planenode may be a core network device or a gateway. The user plane node maybe a SGW, PGW, or a Local GateWay (LGW) for the SAE system, and may be aSGSN or Gateway GPRS Support Node (GGSN) for the UMTS system.

FIG. 2 is a signal flow diagram illustrating a handover operation in aconventional SIPTO and LIPA.

Referring to FIG. 2, a source Base Station (BS) 251 decides to perform ahandover of a UE 250 in step 201.

In step 202, the source BS sends a handover request to a source MME 253.The handover request includes information of a target BS 252, such as anIDentity (ID) of the target BS 252, or a target Tracking Area Identity(TAI), and further includes information such as a target ClosedSubscriber Group (CSG) or handover type.

In step 203, the source MME 253 sends a forward handover request to atarget MME 254. The forward handover request includes information of thetarget BS 252, etc., obtained from the handover request.

In step 204, if re-selecting an SGW for the UE 250, the target MME 254performs a session establishing process with the re-selected target SGW256. Accordingly, step 204 is not executed if the re-selection of theSGW for the UE 250 is not required.

In step 205, the target MME 254 sends a handover request to the targetBS 252, and in step 206, the target BS 252 sends a handover requestacknowledgement message to the target MME 254.

In step 207, the target MME 254 updates carrier information according tothe target BS 252, with which the UE 250 switches, which specificallyincludes the target MME 254 requesting the establishment of a user planetunnel between the target BS 252 and an LGW 257, to ensure the handoverof UE 250 from the source BS 251 to the target BS 252.

Using the conventional handover procedure illustrated in FIG. 2, thereare three common situations that result in handover failure and/or awaste of signaling/wireless resources.

Situation one: The target BS 252 and source BS 251 belong to differentlocal HeNB networks. Thus, the target BS and source BS connect todifferent LGWs 257. As illustrated in FIG. 2, because the target BS 252and source BS 251 connect to different LGWs 257, the handover fails.Further, although the target MME 254 may determine the handover failurewhen establishing the user plane tunnel, and thus, releases theestablished or occupied wireless resources, too many signaling resourcesand wireless resources have already been occupied, thereby wastingsignaling and wireless resources.

Situation 2: The target BS 252 and source BS 251 belong to a same localHeNB network. However, the target BS 252 and source BS 251 connect todifferent LGWs 257, e.g., the target BS 252 and source BS 251 belong todifferent sub-networks, also resulting in the handover failure and thewasting of the signaling and wireless resources.

Situation 3: The target BS 252 and source BS 251 belong to a same localHeNB network, and the target BS 252 and source BS 251 may connect to asame LGW 257. However, the list of LGWs, with which the target BS 252and source BS 251 connect is not the same, e.g., when the target BS 252does not connect to the LGW 257 serving UE 250 at the source end, thisalso results in the handover failure and the wasting of the signalingand wireless resources.

Although, the problems in the conventional handover are described abovewith reference to an S1 handover procedure, if the source BS triggers anX2 handover process, the X2 handover process may fail, and the MME wouldnot determine that the handover will not succeed until receiving a pathswitch request message, also wasting the signaling and wirelessresources.

Furthermore, similar handover problems also exist in UMTS.

Basically, the above-described handover failure refers to the handoverfailure of the LIPA carrier. If a UE merely receives a LIPA service, thewhole handover process performed according to the conventional handoverwill fail. However, if the UE simultaneously receives the LIPA serviceand non-LIPA service, the handover of the non-LIPA service performedaccording to the conventional handover flow may succeed, while thehandover of the LIPA service will fail.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve theabove-described problems occurring in the prior art, and to provide atleast the advantages described below.

Accordingly, an aspect of the present invention is to provide a methodfor avoiding handover failure and excessive resource waste, resultingfrom a failure of the handover process.

In accordance with an aspect of the present invention a method foravoiding handover failure is provided. The method includes determining,by a source Base Station (BS), to perform a handover of a User Equipment(UE); determining, by the source BS, whether a target BS connects with auser plane node serving the UE at the source BS; and releasingresources, when the target BS does not connect with the user plane nodeserving the UE at the source BS.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional SAE system;

FIG. 2 is a signal flow diagram illustrating a handover operation in aconventional SIPTO and LIPA;

FIG. 3 is a flow chart illustrating a handover method in accordance withan embodiment of the present invention;

FIG. 4 is a flow chart illustrating a handover method in accordance withan embodiment of the present invention;

FIG. 5 is a signal flow diagram illustrating a process for exchanginginformation between BSs in accordance with an embodiment of the presentinvention;

FIG. 6 is a signal flow diagram illustrating a process for a BS sendingupdated information to an adjacent BS in accordance with an embodimentof the present invention;

FIG. 7 is a signal flow diagram illustrating a process for an MMEsending information of an LGW selected for a UE to a BS in accordancewith an embodiment of the present invention;

FIG. 8 is a signal flow diagram illustrating a process for an MMEsending information of an LGW selected for a UE to a BS in accordancewith an embodiment of the present invention;

FIG. 9 is a signal flow diagram illustrating a process for the MMEsending information of LGW selected for the UE to a BS in accordancewith an embodiment of the present invention; and

FIG. 10 is a signal flow diagram of illustrating a process for decidingto perform handover in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, specific details such as detailed configuration andcomponents are merely provided to assist the overall understanding ofthese embodiments of the present invention. Therefore, it should beapparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of the present invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

In accordance with an embodiment of the present invention, a method foravoiding handover failure includes determining whether a target BSconnects with a user plane node serving a UE at a source BS, when thesource BS decides to perform a handover of the UE, and releasingresources, if not. More specifically, embodiments of the presentinvention release resources when the target BS does not connect with auser plane node serving the UE at the source BS, when deciding toperform handover of the UE, rather than releasing the sources after ahandover failure, as described above in the background. When the targetBS does not connect with the source user plane node, the bearer to betransmitted through the source user plane node in the subsequenthandover process will fail, and the resources should be released. Theproblem of resource waste resulting from not releasing the resourcesuntil after the handover failure can be avoided by releasing theresources sooner, i.e., after determining that the target BS does notconnect with the user plane node served the UE at the source BS.

The source BS determines whether the target BS connects with the userplane node served the UE at the source BS according to informationexchanged between the source BS and the target BS. The informationexchanged between the source BS and the target BS includes at least oneof information of their local networks, information of their localsub-networks, and information of user plane nodes, with which the sourceBS and the target BS respectively connect.

The information of the local networks includes Local HeNB NetworksIDentifiers (LHN IDs). The information of the local sub-networksincludes the identities of their sub-networks. The information of theconnected user plane nodes may be the information of the connected LGWs.As an example, the embodiments of the present invention will bedescribed below using the connected user plane nodes as the LGWs.

FIG. 3 is a flow chart illustrating a handover method in accordance withan embodiment of the present invention.

Referring to FIG. 3, in Step 301, a source BS and a target BS exchangeat least one of information of their local networks, information oftheir local sub-networks, and information of LGWs, with which theyconnect. For example, the information of the local networks includes LHNIDs, and the information of the local sub-networks includes identitiesof their sub-networks.

Further, there may be one or multiple connected LGWs. If there aremultiple connected LGWs, the information of the connected LGWs includesinformation of the multiple LGWs, such as identities or IP addresses ofthe connected LGWs. The IP addresses of the LGWs may be the IP addressesof LGW control planes, the IP addresses of the LGWs in a core network,or the IP addresses of the LGWs in the local networks.

In step 302, the source BS decides to perform a handover of UE served byitself, determines whether the target BS connects with the LGW currentlyconnected with the source BS, based on the information exchanged betweenitself and the target BS in step 301.

For example, if the information obtained in step 301 is the informationof the local network of the target BS, and the local HeNB network of thesource BS is different from that of the target BS, the source BSconcludes that the LGW connected with the source BS is different fromthat of the target BS because one LGW belongs to a single local HeNBnetwork.

If the information obtained in block 301 includes the information of thelocal sub-network of the BS and/or information of the connected LGWs,and the local HeNB of the source BS is the same as that of the targetBS, the source BS determines whether the source BS and target BS connectto different LGWs based on the information of the local sub-networks ofthe source BS and target BS and/or information of connected LGWs.

When the target BS is connected with the LGW currently connected withthe source BS in step 302, the source BS selects a cell controlled bythe target BS as the target cell of the handover in step 303.

However, when the target BS is not connected with the LGW currentlyconnected with the source BS in step 302, the resources of the local IPaccess bearers are released, if the BS of the target cell selected bythe source BS is not connected with the LGW connected with the source BSin step 304. For example, the source BS triggers the deactivationprocess of the LIPA service, or the source BS sends a message to thesource MME, and the source MME triggers the deactivation process of theLIPA service. Alternatively, the source BS or the source MME sends amessage to the LGW, and the LGW triggers the deactivation process of theLIPA service.

FIG. 4 is a flow chart illustrating a handover method in accordance withan embodiment of the present invention.

Referring to FIG. 4, in step 401 a source BS and a target BS exchangeinformation as described above with reference to step 301.

In step 402, when a UE connects with the BS serving the UE, a corenetwork control plane entity notifies the BS of information of the LGWselected for serving the UE at the BS end. For example, the core networkcontrol plane entity may be the MME or the SGSN. Further, theinformation of the LGW may be an identity or an IP address of the LGW,and the IP address of the LGW may be the IP address of the LGW controlplane, the IP address of the LGW in the core network, or the IP addressof the LGW in the local network.

In step 403, when deciding to perform the handover to the served UE, thesource BS determines whether the target BS is connected with the LGWserving the UE at the source BS end, based on the information of the LGWselected for serving the UE by the core network control plane entity atthe source BS end in step 402 and the information obtained in step 401.

When the target BS is connected with the LGW serving the UE at thesource BS, the source BS selects a cell controlled by the target BS inconnection with the source LGW as the target cell of the handover instep 404.

However, when the target BS is not connected with the LGW serving the UEat the source BS, the resources of the local IP access carriers arereleased, if the BS of the target cell selected by the source BS is notconnected with the LGW connected with the source BS in step 405.

FIG. 5 is a signal flow diagram illustrating a process for exchanginginformation between BSs in accordance with an embodiment of the presentinvention.

Refer to FIG. 5, in step 501, BS 1 (e.g., HeNB1 or eNB1) sends an X2setup request message to BS 2 (e.g., HeNB2 or eNB2). For example, the X2setup request message includes at least one of the information of thelocal network of BS 1, the information of the local sub-network of BS 1,and the information of the LGW, with which BS 1 connects.

In step 502, BS 2 sends an X2 setup response message to BS 1. Forexample, the X2 setup response message includes at least one of theinformation of the local network of BS 2, the information of the localsub-network of BS 2, and the information of the LGW, with which BS 2connects.

Although FIG. 5 is described with reference to an LTE system as anexample, the method therein is also applicable to other systems.

For example, in a UMTS system, the process for exchanging theinformation, for example the information of the their local networks,the information of their local sub-networks, and/or the LGWs, with whichthey connect in the establishment process between the two BSs (e.g., HNBor RNC) through a Iur interface or an Iurh interface is similar to thatof FIG. 5.

When the information of the local network of a BS, the information ofthe local sub-network of the BS, or the LGW, with which the BS connectsis updated, the BS notifies an adjacent BS of the updated information.

FIG. 6 is a signal flow diagram illustrating a process for a BS sendingupdated information to an adjacent BS in accordance with an embodimentof the present invention.

Referring to FIG. 6, in step 601, BS 1 (e.g., HeNB1 or eNB1) sends aneNB configuration update message to BS 2 (e.g., HeNB2 or eNB2). Forexample, the eNB configuration update message includes at least one ofthe information of the local network of BS 1, the information of thelocal sub-network of BS 1, and the LGW, with which BS 1 connects.

In step 602, BS 2 sends an eNB configuration update acknowledgementmessage to BS 1.

FIG. 7 is a signal flow diagram illustrating a process for an MMEsending information of an LGW selected for a UE to a BS in accordancewith an embodiment of the present invention.

Referring to FIG. 7, in step 701, The UE 750 sends a Non Access Stratum(NAS) message, such as an Attach message or Packet Data Network (PDN)connection request message, to the S-HeNB 751.

In step 702, the S-HeNB 751 sends the NAS message received from the UE750 to the MME 753 through an S1 Access Protocol (AP) message. In thesituation with the HeNB GW deployed, the S-HeNB 751 sends the S1 APmessage to the MME 753 through the HeNB GW.

In step 703, the MME 753 performs the NAS authentication/securityprocess between itself and the UE 750, after receiving the NAS message.Specific methods for performing the NAS authentication/security processare known in the art.

Further, the authentication and NAS security for activating integrityprotection is performed when there is no UE context of the UE 750 in thenetwork, when there is no integrity protection of the Attach request insteps 701 and 702, or when the integrity authentication fails; otherwisethe process is optional. When the NAS security algorithm is changed, theNAS security establishment is performed in step 703.

The MME 753 continues with the Attach process when skipping theauthentication and security establishment process or accepting theauthentication failure, if the MME 753 is configured with the emergencyAttach supporting no authentication IMSI, and the UE 750 indicates thatthe Attach type is emergency.

In step 704, the MME 753 sends an initial context setup request messageto the S-HeNB 751. Specifically, with the HeNB GW deployed, the MME 753sends the initial context setup request message to the S-HeNB 751through the HeNB GW.

As for the LIPA service, the core network selects the LGW serving the UE750 for the UE 750 with a method based on the Radio Access Network(RAN), Domain Name System (DNS), or other methods. However, the specificmethod for selecting the LGW is not the focus of these embodiments ofthe present invention, and detailed descriptions thereof are omittedhere.

The initial context setup message includes the information of the LGWselected for the UE, such as the identity or IP address of the LGW.After receiving the initial context setup request message, the S-HeNB751 saves the received information of the LGW.

In step 705, after receiving the initial context setup request message,the S-HeNB 751 establishes a wireless bearer with the UE 750.

In step 706, the S-HeNB 751 sends an initial context setup responsemessage to the MME 753.

With the HeNB GW deployed, the initial context setup response message issent to the HeNB GW, and the HeNB GW sends the initial context setupresponse message to the MME 753.

Accordingly, in a UMTS system, the SGSN that notifies the BS of theinformation of the LGW, such as the identity or IP address of the LGW,selected by the core network for the UE through the RAB allocationrequest message, when the UE accesses the BS.

Further, the source BS is notified of the information of the user planenode selected for serving the UE at the source BS end through an EvolvedRadio Access Bearer (E-RAB) setup message. This replaces the initialcontext setup request message with the E-RAB setup request message andreplaces the initial context setup response message with the E-RAB setupresponse message.

FIG. 8 is a signal flow diagram illustrating a process for an MMEsending information of an LGW selected for a UE to a BS in accordancewith an embodiment of the present invention.

Referring to FIG. 8, the source BS 851 decides to make a handover instep 801.

In step 802, the source BS 851 sends a handover request to the sourceMME 853. For example, the handover request includes information of atarget BS 852, such as the ID and Tracking Area ID (TAI) of the targetBS 852 and may further include information such as the target CSG or ahandover type.

In step 803, the source MME 853 sends a forward handover request to thetarget MME 854. The forward handover request includes the information ofthe target BS 852 obtained from the handover request. The message mayfurther include information of the LGW 857 selected for the UE 850 atthe source end, such as the identity or IP address of the LGW 857.

In step 804, if re-selecting the SGW for the UE 850, the target MME 854performs a session establishment process with the re-selected target SGW856. If the SGW for the UE 850 is not re-selected, step 804 is notexecuted.

In step 805, the target MME 854 sends a handover request to the targetBS 852. The handover request message includes the information of theuser plane node selected for the UE 850, such as the information of theLGW 857. The information of the LGW 857 may be the identity or IPaddress of the LGW 857. The target BS 852 saves the received informationof the user plane node, such as the information of the LGW 857.

In step 806, the target BS 852 sends a handover request acknowledgementmessage to the target MME 854.

In step 807, other existing handover processes continue.

Accordingly, in the UMTS system, the SGSN notifies the BS of theinformation of the user plane node selected for the UE by the corenetwork, such as the information of the LGW through a relocation requestmessage when the UE accesses the BS for the first time through arelocation process. The information of the LGW includes the identity orIP address of the LGW. The detailed technical descriptions are omittedhere.

FIG. 9 is a signal flow diagram illustrating a process for the MMEsending information of LGW selected for the UE to a BS in accordancewith an embodiment of the present invention.

Referring to FIG. 9, in step 901, the S-HeNB 951 makes a handoverdecision.

In step 902, the S-HeNB 951 sends a handover request message to a T-HeNB752.

In step 903, the T-HeNB 952 sends a handover request response message tothe S-HeNB 751.

In step 904, the S-HeNB 951 sends an RRC connection re-configurationmessage to the UE 950, requesting the UE 950 to perform the handover.

In step 905, after finishing the handover, the UE 950 sends an RRCconnection re-configuration completion message to the T-HeNB 952.

In step 906, the T-HeNB 952 sends a path switch request message to anHeNB GW 953, and the HeNB GW 953 sends the path switch request messageto an MME 954. In this step, the T-HeNB 952 may directly send the pathswitch request message to the MME 954, if the T-HeNB 952 does not accessthe MME 954 through the HeNB GW 953.

In step 907, the MME 954 sends a modification bearer request message toan SGW/PDN GW 955.

In step 908, after finishing the modification of the bearer of the UE950, the SGW/PDN GW 955 sends a modification bearer response message tothe MME 954.

In step 909, the MME 954 sends a path switch request acknowledgementmessage to the HeNB GW 953, which sends the path switch requestacknowledgement message to the T-HeNB 952. In this step, the MME 954directly sends the path switch request acknowledgement message to theT-HeNB 952, if the T-HeNB 952 does not access the MME 954 through theHeNB GW 953.

For example, the path switch request acknowledgement includes theinformation of the LGW selected for the UE 950. The information of theLGW 950 may be the identity or IP address of the LGW 950. The T-HeNB 952saves the received information of the user plane node, such as theinformation of the LGW 950.

In step 910, the T-HeNB 952 sends a resource release message to theS-HeNB 951, after receiving the path switch request acknowledgementmessage.

In the UMTS system, the source BS notifies the target BS of theinformation of the LGW selected for the UE by the core network using arelocation request message or handover request message, when the UEaccesses the BS for the first time through an optimized relocationprocess. The information of the LGW includes the identity or IP addressof the LGW.

FIG. 10 is a signal flow diagram of illustrating a process for decidingto perform handover in accordance with an embodiment of the presentinvention.

Refer to FIG. 10, in step 1001, an S-HeNB 1051 makes a handoverdecision. The S-HeNB 1051 may consider whether the target T-HeNB 1052 ofthe target cell connects with an LGW currently serving a UE 1050, whenselecting the target cell.

Whether target T-HeNB 1052 of the target cell connects with the LGWcurrently serving the UE 1050, is described above.

In step 1002, if the target T-HeNB 1052 of the selected target cell doesnot connect with the LGW serving the UE 1050 at the source end, theS-HeNB 1051 releases the resources, such as triggers the release ordeactivation process of the LIPA service. Alternatively, the S-HeNB 1051sends a message, such as an E-RAB release indication to the source MME,and the source MME triggers the deactivation process of the LIPAservice.

Alternatively, the source BS or MME sends a message to the LGW, and theLGW triggers the deactivation process of the LIPA service. Otherdeactivation processes may be adopted, which does not affect the maincontents of the present invention.

In accordance with the above-described embodiments of the presentinvention, a source BS determines whether a target BS connects with auser plane node, such as an LGW, which serves the UE at the source BSend, when deciding to perform a handover of the UE. If a result of thedetermination is no, the LIPA bearer handover will likely fail, and theLIPA bearer resources are released. That is, the occupied signaling andwireless resources are released in advance, rather than being releasedafter the handover failure, as described in the background. Accordingly,the above-described embodiments of the present invention preventresource waste and improve system performance.

While the present invention has been particularly shown and describedwith reference to certain embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims and theirequivalents.

1. A method for avoiding handover failure, the method comprising:determining, by a source Base Station (BS), to perform a handover of aUser Equipment (UE); determining, by the source BS, whether a target BSconnects with a user plane node serving the UE at the source BS; andreleasing resources, when the target BS does not connect with the userplane node serving the UE at the source BS.
 2. The method of claim 1,further comprising exchanging, between the source BS and the target BS,connection information including at least one of information of localnetworks of the source BS and the target BS, information of localsub-networks of the source BS and the target BS, and information of userplane nodes with which the source BS and the target BS connect.
 3. Themethod of claim 2, wherein the source BS determines whether the targetBS connects with the user plane node served the UE at the source BS,based on the information exchanged between the source BS and the targetBS.
 4. The method of claim 2, further comprising notifying, by a controlplane entity of a core network, the source BS of information of the userplane node selected for serving the UE at the source BS end.
 5. Themethod of claim 4, wherein the source BS determines whether the targetBS connects with the user plane node serving the UE at the source baseend, based on the information of the user plane node serving the UE atthe source BS end and the information exchanged between the source BSand the target BS.
 6. The method of claim 4, wherein the control planeentity of the core network notifies the source BS of the information ofthe user plane node selected for servicing the UE at the source BS endthrough one of an initial context setup request message, an EvolvedRadio Access Bearer (E-RAB), a setup request message, and a Radio AccessBearer (RAB) assignment message, when the UE accesses a service throughthe source BS.
 7. The method of claim 4, wherein the control planeentity of the core network notifies the source BS of the information ofthe user plane node selected for serving the UE at the source BS endthrough a handover request message when the UE initially accesses thesource BS for through an S1 handover.
 8. The method of claim 4, whereinthe control plane entity of the core network notifies the source BS ofthe information of the user plane node selected for serving the UE atthe source BS end through a path switch request acknowledgement messagewhen the UE initially accesses the source BS through an X2 handover. 9.The method of claim 4, wherein exchanging information between the sourceBS and the target BS comprises: sending, by one of the source BS and thetarget BS, at least one of information of a local network, informationof a local sub-network, and information of the user plane node, withwhich one of the source BS and the target BS connects, carried in an X2setup request message; sending, by the other one of the source BS andthe target BS, at least one of information of a local network,information of a local sub-network, and information of the user planenode, with which the other one of the source BS and the target BSconnects, carried in an X2 setup response message to the one of thesource BS and the target BS.
 10. The method of claim 4, whereinexchanging information between the source BS and the target BScomprises: obtaining, by the source BS and the target BS, at least oneof information of a local network of a peer, information of a localsub-network of the peer, and information of a user plane node, withwhich the peer connects in an establishment process of an lur or Iurhinterface.
 11. The method of claim 4, further comprising: notifying anadjacent BS of updated information when the connection informationupdates.
 12. The method of claim 11, wherein the updated information isnotified to the adjacent BS through an eNB configuration update messageduring an update process of an lur interface or an update process of anIurh interface.
 13. The method of claim 1, wherein releasing theresources comprises triggering, by the source BS, a deactivation processof a Local IP Access (LIPA) service.
 14. The method of claim 1, whereinreleasing the resources comprises: sending, by the source BS, a messageto a source Mobility Management Entity (MME); and triggering, by thesource MME, a deactivation process of a Local IP Access (LIPA) service.15. The method of claim 1, wherein releasing the resources comprises:sending, by the source BS or a source Mobility Management Entity (MME),a message to a Local GateWay (LGW); and triggering, by the LGW, adeactivation process of a Local IP Access (LIPA) service.
 16. The methodof claim 2, wherein the information of the local network includes aLocal Home evolved NodeB Network IDentifier (LHN ID).
 17. The method ofclaim 2, wherein the information of the local sub-network includes anidentity of the local sub-network.
 18. The method of claim 2, whereinthe information of the user plane nodes includes information ofconnected Local GateWays (LGWs).
 19. The method of claim 18, wherein theinformation of the connected LGWs includes identities or InternetProtocol (IP) addresses of the LGWs.